The present invention relates to a high-molecular weight phosphorus-containing polyester flame retardant and its synthesis.
Polymeric resins which are flame retardant and are resistant to high temperatures, can be obtained by incorporating flame retardant comonomers (flame retardant) onto the backbones of the polymers by copolymerization. As the flame retardants are chemically bonded to the polymeric backbones, they will not migrate to the surfaces of the polymeric resins during processsing, such as extruding or injection molding, and thus the flame retarding effect and physical properties are not affected. Washing fastness is also good when the polymeric resins are woven into fabrics or nonwoven fabrics. However, this method necessitates producer-treatment at increased cost.
Another method which can be customer-treated, is to coat a layer of flame retardants on fabricated articles of polymeric resins. For example, flame retardants can be coated on fabrics to render such fabrics flame resistant. However, the flame retarding effect will gradually diminish with repeated washings. That is, the washing fastness of thus treated fabrics is generally unsatisfactory.
Polymer blending is another method adopted to improve the flame reistance of polymeric resins. Polymeric resins are blended with flame retardants before they are fabricated into shaped articles, such as fibers and filaments. This method has the advantage of easy manufacture. However, organic flame retardants usually can not endure processing at an elevated temperature. For example, polyester and polyamide usually are extruded into filaments at a temperature higher than 290.degree. C., and thus the high temperature often makes organic flame retardants degrade, resulting in breakage of filaments. If polymeric resins are blended with inorganic flame retardants, when spinning, the spinnerets will be blocked. This affects the pack pressure in spinning, resutling in a high rate of occurrence of broken and short filaments. In addition, poor compatability between polymers and flame retardants often causes the migration of flame retardants when the blend is processed, especially at elevated termperatures. The washing fastness of the fabrics is also unsatisfactory if the fabrics are prepared from flame resistant fibers by polymer blending.
Recently, phosphorus-containing and large molecular flame retardants have been developed to replace conventional halogen-containing flame retardants to meet the requiremets of low toxicity, low smoke and low migration in view of environment protection and public security. For example, CR733 of Daihachi Chemical Industry Co., Ltd, and RDP of AKZO Co., Ltd, are phosphate flame retardants having a polymerization degree of less than 15 and a molecular weight of less than 2000. However, the heat resistance of these phosphate flame retardants is still not satisfactory, and said fabrics are only suitable for adding to polymeric resins to be processed at a relative low temperature, in such applications as, for example polyurethane foams, polyurethane leathers, polyurethane paints, and flexible PVC. Phosphonic anhydride flame retardants produced by Hoechst Celanese Corp. and TOYOBO's GH flame retardants also display unsatisfactory heat resistance. And because they are reactive flame retardants, they are added to polyester resins and subject to copolymerization. The resulting copolyesters contain 0.4-0.7 wt % of phosphorus and are suitable for being spinned into flame resistant fibers or filaments. High molecular weight polyphosphoric ammoninum-containing flame retardants have been developed by Monsanto Co. and Hoechst Celanese Corp., however these ammoninum polyphosphate have poor compatability with polyester, and are only resistant to a temperature of about 200.degree. C.